The present invention is directed to a device for bone tissue removal, and in particular to a device having a detachable head for expedited reaming of a medullary canal.
A wide variety of devices for cutting and removing bone tissue are known in the art. In general, these devices utilize a rotating cutting tip, similar to a drill, located at a distal end of a drive shaft. Bone cutting devices for use in reaming the medullary canal typically use a flexible drive shaft because the medullary canals of bones are seldom straight and usually will have some degree of curvature. Most reamers also have a central bore through both the reamer and the drive shaft. The central bore is intended to receive a long, small diameter guide pin or wire which is initially inserted into the medullary canal to act as a track for the advancing reamer.
Reamers are used in orthopedic surgery to prepare the medullary canals of bone for a wide variety of surgical procedures including total hip and knee replacement, nail insertion for stabilization of a long bone fracture, intramedullary osteotomy, and bone harvesting for grafting purposes.
From both a mechanical and a biological point of view, medullary reaming is particularly beneficial in improving the performance of implants. Specifically, reaming expands the medullary canal so that larger diameter implants can be inserted. These larger diameter implants are less likely to fail. In fact, certain fractures require over-reaming so that larger implants can be used. Without reaming, the surgeon must use a xe2x80x9cbest guessxe2x80x9d estimate when selecting the diameter of the implant. The medical literature contains numerous case studies reporting the adverse consequences of an inaccurate estimate. Reaming provides a direct measurement of the diameter of the medullary canal, and thereby allows for the selection of an implant that precisely fills the canal. As a result, the stability of the fracture site is enhanced by achieving endosteal contact. When implants do not fill the medullary canal, load sharing between the implant and the bone is decreased. This increases the load that is transferred to the implant and promotes both implant failure and stress shielding of the bone.
Despite such benefits, negative consequences have also been associated with medullary reaming. In particular, current procedures for reaming the medullary cavity can result in an increase in both temperature and pressure. Like most any process in which material is being removed, reaming causes generation of heat. Furthermore, a hydraulic pressure, which far exceeds that of blood pressure, builds up in the cavity during reaming. The reamer acts as a hydraulic piston within the bone cavity, and if the contents of the canal, which include a mixture of medullary fat, blood, blood clots, and bone debris, enter the blood stream, an embolism can result. Excessive heat has been associated with an increased incidence of aseptic necrosis of the cortex and elevated pressure has been associated with an increased risk of fat emboli. These complications are more likely to occur in patients when extenuating factors such as shock, existing lung contusion, multiple traumas, or pre-existing pulmonary impairment are present. In these situations, the preferred method of reaming would usually not be performed due to the increased risks involved.
Various devices and methods exist for reducing the intramedullary pressure build-up during reaming. For example, in prosthetic joint replacement, a distal venting hole, a large insertion hole, and a modified technique for cement insertion have all been shown to have some success in reducing pressure, and presumably, the chance of fat embolism. Venting holes in the bone only have little effect because their diameter is typically too small and local peak values must be assumed during the passage of the reamer. Similarly, reaming the medullary cavity less does not prevent pressure increase. In fact, pressure can be high even for reamers of small diameter.
Another technique which has been used in an attempt to reduce temperature and pressure is to perform the reaming in multiple steps with increasing size of reamers with each step. As a result, reaming procedures are done slowly with the application of gentle pressure and requiring multiple passes. Usually reaming is performed in 1 mm diameter increments until the bone cortex is reached and then in 0.5 mm increments thereafter. In this regard, the reaming is carried out with less compression force and the intramedullary pressure can be easily reduced with most reaming devices utilizing this slow process. A faster reaming process utilizing fewer passes would be desirable in order to reduce operating time and medical costs.
The reaming device disclosed in U.S. patent application Ser. No. 09/495,932 entitled xe2x80x9cSurgical Reamer and Method of Using Samexe2x80x9d filed on Feb. 2, 2000, the entire contents of which is expressly incorporated herein by reference, allows reaming of a medullary canal at an enhanced rate without the negative consequences associated with medullary reaming such as increasing the risk of fat emboli and heat necrosis upon cutting and removal of bone tissue. Furthermore, the reaming device can be single use so after the surgical procedure is completed, the flexible aspiration tube along with the fixed reamer head can be discarded.
By having a single use reaming device, the problems associated with the reamer head becoming blunt over time are avoided. For example, the problems of greater intramedullary pressures and greater increases in cortical temperature resulting from the continued use of a blunted reamer are avoided. In addition, by having a single use reaming device, the careful attention of surgeons and operating staff to treat the reamers gently is not necessary.
However, there are some drawbacks to having a single use reaming device with a fixed reamer head. Typically, the anatomy of patients will vary requiring different reamers and reamer heads to accommodate the variance in the patient anatomy. For example, some patients will have larger long bones which may require larger reamer heads. Since the reamer head is fixed to the rest of the reaming device, the surgeons and operating staff would have to maintain a full inventory of different reamers to accommodate the different patient anatomies. Maintaining a full inventory of reamers would require a lot of space and would be costly. As a result, a single use reaming device with a detachable reamer head is desirable to avoid the problems of having to maintain a full inventory of reamers. By having a detachable reaming head, the surgeon and operating staff would have to maintain only a few reaming devices with a full inventory of reaming heads. This would require less space and would be less costly.
In addition, reamer heads generally are durable and a few uses will not impair the reliability or efficacy of the reamer head. Accordingly, having a detachable reaming head allows for future re-use of the reamer head thereby reducing the cost associated with the reaming procedure.
Thus, there exists a need for a device for reaming a medullary canal at an enhanced rate without increasing the risk of fat emboli and heat necrosis upon cutting and removal of bone tissue and which allows the reamer head to be detached for future re-use.
The present invention relates to a device for reaming a medullary canal of a bone. The device includes a rotatable drive shaft connected at the proximal end to a rotational drive element and a detachable reamer head rotatably coupled to the distal end of the drive shaft. The reamer head has a tubular shank with resilient arms coupling to the distal end of the drive shaft and a cutting head integral with the shank and having a plurality of blades. Flutes are located between adjacent blades.
The drive shaft and reamer head each may have a cannulation. These two cannulations are aligned when the tubular shank and the resilient arms are engaged with the drive shaft to form a center channel. One use for this channel is for receiving a guide wire that can be used to direct the device in the medullary canal.
The device may also include an aspiration tube for removing cut material generated by the reamer head. The aspiration tube has a manifold assembly at a proximal end and a lumen configured and dimensioned to receive the drive shaft. The aspiration tube also is connected to a reamer head retainer via a retaining ring at a distal end. Preferably, the center channel is in fluid communication with an irrigation source to provide irrigation to the cutting head. The manifold assembly may include an irrigation port connected to the irrigation source and an irrigation chamber in fluid communication with the irrigation port. The irrigation fluid travels from the irrigation chamber through an opening on the drive shaft and into the center channel.
The reamer head retainer rotatably engages the reamer head via an internal shoulder and the reamer head resilient arms. The reamer head retainer further has a plurality of ports which are in fluid communication with the flutes of the reamer head and the distal end of the lumen of the aspiration tube. The proximal end of the lumen of the aspiration tube is in fluid communication with a suction source. Preferably, the manifold assembly includes an aspiration port connected to the suction source to assist in the removal of the cut material.
The invention also relates to removing the reamer head from the reamer head retainer for future re-use by using a reamer head removing device. The reamer head removing device engages the resilient arms of the reamer head disengaging the resilient arms from the reamer head retainer thereby allowing the reamer head to be detached from the reamer head retainer.